During a typical installation of a window in a building, a rough opening is first prepared in a wall of the building for receiving the window. The rough opening is defined by two jambs that extend vertically from a head at the top of the rough opening to a sill at the bottom of the opening. In some cases, a weather resistant barrier material, such as a thin sheet of waterproof paper or plastic is disposed over the outer surface of the wall, and the barrier material is cut at the rough opening and folded into the opening. The barrier material forms a moisture barrier extending over the outer surface, but, due to the cuts, the barrier material does not normally provide a waterproof barrier on the inner surfaces of the rough opening. In particular, the barrier typically defines openings at the intersection of the jambs and the sill where the barrier material is cut to allow folding thereof. In some cases, a rigid sill flashing can be installed across the sill. The sill flashing extends outward from the sill onto a portion of the outer surface of the wall and upward from the sill onto a portion of each jamb. Thus, the sill flashing, which is formed of a flexible sheet of material such as metal, is cut and bent to correspond to the sill, jambs, and outer wall surface. Typically, two cuts are made in the sill flashing, each cut extending from a respective corner of the sill and the jambs through the portion of the sill flashing that is disposed on the outer surface of the wall. Thereafter, the flashing is welded to seal the cuts in the flashing at the corners of the opening.
The window can be structured to prevent rain or other water contacting the outer surface of the window from flowing to the sill of the rough opening. However, in some cases, the window can leak water to the sill. Water flowing to the sill of the rough opening can sometimes penetrate both the barrier material and the flashing, e.g., through the cuts that are made in the barrier material and the flashing during installation. Thus, the water can flow into the wall, i.e., between the inner and outer surfaces of the wall, causing damage to the wall.
U.S. Pat. No. 7,059,087, invented by the present inventor, describes a flashing that can be disposed at the corner of an opening in a wall, e.g., under a window or other portal, to prevent the entry of water at the corner. U.S. Patent Application Publication No. 2005/0166471, also invented by the present inventor, describes methods for using such flashings and further describes the use of such flashings with a laminar moisture barrier sheet disposed on the outer surface of the wall. In some cases, first and second flashings can be disposed, respectively, at the two lower corners of an opening in a wall, and a third flashing can be disposed therebetween. The interfaces of the flashings can be covered with tape to prevent water from passing through the interfaces to the sill of the opening. While these flashings and methods provide important improvements, further improvements are desirable.
Some conventional flashing members that are provided at the sill of an opening include a lower portion that is disposed beneath the window and a back dam that extends vertically upward from lower portion at the inside edge of the lower portion. U.S. Pat. No. 1,677,130 describes a sill flashing that includes an intermediate flashing 19 and an upstanding flange 31 on the rear edge thereof. The upstanding flange 31 extends upward above the top of the intermediate flashing 19 and in contact with the side of the sill 14 of the window. While such back dams generally decrease the likelihood of water passing under the sill and into the building, the back dam can increase the complexity of the installation of the window.
For example, during a typical window installation, the window is placed in the opening of the wall (from the outside) and then shims are selectively inserted (from the inside) under the window to adjust the window to a desired placement, e.g., to raise the window slightly or to adjust the sill of the window to a horizontal configuration. However, as shown in FIG. 1 of U.S. Pat. No. 1,677,130, the upstanding flange 31 prevents the insertion of shims between the flashing and the sill 14 from the rear, i.e., the interior of the building. Further, since the flashing is disposed in the opening and nailed in place before the window is positioned, shims cannot be inserted below the flashing without removing the window and flashing or deforming the flashing. Thus, the back dam prevents or complicates the use of shims for adjusting the window after the window is placed in the opening. In some cases, the window must be removed in order to place the shims on the flashing, or the installer may simply omit the shims, such that the window may not be properly horizontally positioned.
In addition, a conventional method for installing a window includes installing drywall on the interior surface of the wall after the flashing (and, typically, the window) is installed. The drywall is installed in large sheets, and typically the sheets are not precut with holes for the window. That is, an installer typically installs the drywall to partially or completely cover the window opening, and only then cuts the drywall to remove the portion at the opening of the window. In one typical method, the window is installed in a wall opening that has rough dimensions (in width and height) that are at least one-half inch greater than the outer dimensions of the window. This relative difference in size between the window and the opening provides space for the insertion of shims around the window and typically results in a small space or gap around the window. An installer can use this gap as a guide for cutting the drywall. For example, with the window installed and the drywall installed to at least partially cover the opening, the installer can use a router to cut the drywall around the periphery of the window, using the space between the periphery of the window and the opening as a guide for the bit of the router. Unfortunately, when the router is moved against a flashing, the router may cut through the flashing. In particular, if the sill flashing is disposed tightly against the sill and jambs of the opening, the installer will typically move the router bit downward along one of the jambs of the opening toward the sill, between the window and the flashing. As the router contacts the back dam of the flashing, the back dam can be cut or otherwise damaged, thereby potentially reducing the effectiveness of the back dam for preventing water intrusion.
Further, a conventional back dam extends upward beyond the bottom of the window and is disposed against the inside surface of the window, such that the height of a conventional back dam is restricted by the configuration of the window. For example, the back dam typically cannot have a height that is greater than the height of the bottom frame or sill of the window, as a higher back dam would extend upward beyond the bottom frame resulting in an aesthetically undesirable appearance. Further still, the location of the back dam against the inside surface of the window adds to the thickness of the window frame at the bottom of the window such that the inside surface of the window frame at the top and sides of the window is not coplanar with the inside surface of the back dam at the bottom of the window. Thus, if a planar member, such as an interior wood frame or a sheet of drywall, is disposed against the inside surface of the window, the additional thickness of the back dam at the bottom of the window results in a gap between the planar member and the window frame at the sides and top of the window. Such a gap reduces the aesthetic appearance of the window installation and/or complicates the installation by requiring additional steps for eliminating or covering the gap.
Thus, there exists a continued need for improvements to such flashings, for example, to facilitate the proper installation of the flashings and to further reduce the likelihood that water will flow to the rough opening in the wall and to the inside of the wall.